A convincing mechanism for the development of insulin resistance with the development of obesity has not yet been determined. A recent report has indicated that fasting plasma insulin concentration,a measure of insulin resistance is correlated with muscle phospholipid polyunsaturated fatty acid content. A similar relationship is also found with obesity. In a collaborative study with the authors of this work, we will examine the relationship of obesity, insulin resistance and membrane phospholipid content in Pima Indians to determine if obesity leads to insulin resistance by altering membrane phospholipid content.